Charles's income from the Duchy of Cornwall, a portfolio of land, property and investments, was up 4% to a record level of £19 million.

The Prince's tax bill fell slightly by £70,000 to £4.426 million, a drop of 1.5%.

Prince Charles speaks to families at an Army Rehabilitation centre in Birmingham Credit: ITV News

William Nye, Charles's principal private secretary, speaking during a press briefing about the annual review, said: "Naturally we're happy to appear before the Public Accounts Committee, if they would like to see us."

He added: "The Duchy estate provides an income for the heir to the throne, there are some special rules that apply to it.

"The Prince of Wales gets the income from the Duchy but he doesn't have access to the capital, that's always been the case."

The Prince of Wales poses for photographs with local youths who take part in Prince's Trust activities Credit: Jonathan Brady/PA Wire

Mr Nye went on to say that Charles funds the majority of the official costs of himself and immediate family - the Duchess of Cornwall, Duke and Duchess of Cambridge and Prince Harry - and although exempt from income tax pays it voluntarily on his Duchy income.

Asked to comment on claims that the Duchy should pay corporation tax, he replied: "It's not a corporation so it doesn't pay corporation tax, it's owned by the Duke of Cornwall and he gets the income and then he pays income tax, like anybody else who owns some property from which they gain an income."

He added: "The whole point about the Duchy is that it is set up specifically, and indeed required by law, to maintain its capital, to roll over and maintain its capital and to invest in the future to generate income for the future."